The long-range goal of this proposal is to furnish a new rationale for improving the treatment of human leukemias with arabinonucleosides. The research will build on knowledge that T and B lymphoblasts differ in their ability to metabolize purine deoxyribonucleosides via deoxycytidine (dCyd) kinase and adenosine (Ado) kinase. We have demonstrated a highly significant correlation between the level of the two enzyme activities, dCyd kinase and Ado kinase, and the loss of clonogenic capacity of cultured human T lymphoblasts (CCRF-CEM) exposed to purine analogs; 9-beta-D-arabinofuranosyladenine (ara-A) and its adenosine deaminase resistant analog, 2-fluoro-ara-A. The cytotoxicity and biochemical properties of the latter two compounds will be compared with those of two newer analogs, 2'-o-nitro-ara-A and 2'-azido-ara-A, modified in the pentose moiety, in cultured human lymphoblastoid of T- and B-cell origin. In particular, we propose to define (a) the role of specific kinases in the activation of purine deoxyribonucleosides and that of pharmacologically active analogs, (b) whether there is a differential pattern of nucleoside kinase utilization for the activation of the natural purine dAdo and ara-A analogs to cytotoxic nucleotides in T vs. B lymphoblasts and (c) the molecular sites of action of these arabinonucleoside analogs in the human leukemia cells. Differences in metabolic activity will be distinguished by the use of mutants with distinct defects in nucleoside kinase activities. All lines of human lymphoblasts required for the study are available in our laboratory in quantities necessary to perform biochemical analyses and to isolate functional components, such as enzymes. The cytotoxicity of the arabinonucleosides will be compared by clonogenic assays or growth inhibition studies; the formation and flux of the active analog nucleoside 5'-tri-phosphates will be determined by high-pressure liquid chromatography (HPLC). The relationship between the action of the analog triphosphate and cellular deoxyribonucleotides will be determined by HPLC and the inhibition of discrete steps of DNA synthesis.